CHAPTER 4

WEAVING PREPARATION
4.1 Importance of weaving preparation
Weaving is a convenient way of describing the series of processes
that convert yarn into loom-state fabric, which is then inspected
and prepared for the finishing processes or loom state use.

Figure 4.1 shows the major steps in fabric production.

Figure 4.1 Major Steps in Fabric Production.

In general, the subdivision of fabric production into three process

groups Spinning, Weaving, and Finishing
Yarn is the basic building block in weaving. Therefore, after yarn
1
manufacturing, the next step would be to weave the yarn into a
fabric.

However, in practice, the condition of yarn produced on the

spinning machine is not always good enough to be used directly
for fabric formation.

Package size, yarn surface characteristics, and other factors make

it necessary for both weft yarn and warp yarn to be further
processed for efficient fabric formation. These preparatory
processes are called weaving preparation, which is the subject of
this course.

The object of preparatory processes is to prepare packages of a

size and build best suited to a particular purpose.

For maximum efficiency, yarn breakage at the loom must be

reduced to a minimum and this is only possible if:
(a) care is taken to select yarn of uniform quality;
(b) the yarn is wound on to a suitable package in the best possible
way;
(c) the yarn has adequate treatment before use.

Warp and filling (weft) yarns are subjected to different conditions

2
and requirements during weaving. Therefore, the preparation of
warp and filling yarns is different.

Warp yarn is subjected to higher stresses, which requires extra

preparation. The filling yarns are not subjected to the same type of
stresses as the warp yarns and thus are easily prepared for the
weaving process.

The yarn is marketed wound on various types of packages, which

generally depend on the technology of the spinning process from
which the yarn originates; the most common packages are cones
(either cones or bicones, or tubes, or tricones), pools or bobbins,
flanged bobbins, hanks and cheeses.

Figure 4.2 shows the major preparation processes for weft and
warp yarns.

3
 Figure 4.2 Weaving preparation process
Spun yarn quality characteristics that are most important for good
weaving performance include short- and long-term weight
uniformity, imperfections, tensile properties and hairiness.

4.2 Warp Preparation

The essential features of a good warp are as follows:
• The yarn must be uniform, clean, and as free from knots as
possible.

4
 • The yarn must be sufficiently strong to withstand the stress
and friction of weaving without excessive end breakage.

• Knots should be of standard type and size, enabling them to

pass easily through the heddles and reeds of the loom.

• The warp must be uniformly sized and the amount of size

added must be sufficient to protect the yarn from abrasion at
the heddles and reed so as to prevent the formation of a hairy
surface on the warp threads.

• The ends of the warp must be parallel and each must be

wound on to the loom beam at an even and equal tension;
also, each warp end must be of the correct length and there
should be no broken end therein.

The object of warp preparation is to transfer yarn from the

spinners Package to a weaver’s beam that can be placed behind
loom ready for weaving.

It is usual to divide the warp preparation processes into the five

sections (Winding, Beaming, Sizing, Drawing-in, and Tying-in)
described in the following pages.

5
4.2.1 Warp Winding (Coning)
One of the main purposes of warp winding is to transfer yarn from
the spinner’s or doubler’s package (Fig. 4.3(a)) to another suitable
for use in the creel of a warping machine (Fig. 4.3(b)) or for
dyeing.

Figure 4.3
A second main purpose of warp winding is to make it possible to
inspect the yarn and to remove any thick or thin laces slubs, neps
or loose fibers (Fig. 4.4).

6
 Figure 4.4 Some typical yarn faults.

It is an important and necessary process that performs the follow-

ing functions

a) Winding produces a yarn package that is suitable for further

processing (Package size).

The amount of yarn on several small packages is combined by

splicing or knotting onto a single package (Figure 4.5).

Figure 4.5 Building large packages

b) The winding process provides an opportunity to clear yarn

defects (clearing).

Thin and thick places, slubs, neps or loose fibers on the yarn are

7
 cleared during winding and, thus, the overall quality of the yarn
is improved. (Figure 4.4).

The operation of removing these undesirable elements of yarn,

called clearing.

Staple yarns require this clearing operation most because they may
have these kinds of faults more often.
c) Package Build

Sometimes the yarn has to be dyed or otherwise treated between

spinning and weaving. In such cases it is usually necessary to
wind the yarn on a special package to permit this treatment.

In the case of dyeing, the package must allow even penetration of

dye so that all parts of the yarn are similarly treated. The tube or
cone on which the yarn wound is usually perforated, the yarn is
wound rather less tightly than normal and the build is such as to
create many interstices through which the dye may pass.

The cost of rewinding has to be weighed against the extra cost of

using a less dense packages which might be of an unsuitable
shape.

8
4.2.1.1 Winding Requirements
The requirements for winding may be summarized as follows:

(i) The fault level in the yarn must be reduced to an acceptable

level.

(ii) The yarn must not be damaged in any way in the winding
process.
(iii) The yarn must be wound in such a way as to permit
unwinding in the following processes with a minimum ‘of
difficulty at the required speeds.

(iv) The package size, shape, and build must be the most
technologically suitable for the particular end use.
(v) The package size should be controlled to meet the particular
economic requirements.
(vi) The winding operation must be geared to give the best
possible economic performance of the whole process of fabric
manufacture.
4.2.1.2 Winding Process
The normal winding operation consists of unwinding one package
and rewinding onto another.

But, there are three main regions in winding (Figure 4.6). These
are unwinding, package stability (tensioning and clearing zone),
9
and winding.

Figure 4.6 Winding process

I-Unwinding of yarn from the spinning package

The yarn package is held in the creel in an optimum position for
unwinding. Yarn withdrawal can be done in two ways (Figure 4.7)

10
 Figure 4.7 Yarn withdrawal

a) Side withdrawal.

In this method the spool is rotated and therefore the yarn does
not rotate during withdrawal. As a result, the yarn twist does not
change, which is an advantage.

Since the yarn does not rotate, the spool must rotate for side
withdrawal. This requires additional energy and equipment,
which is a disadvantage.

Due to inertia, the rotation of the spool can cause yarn tension
variations.

11
 Side unwinding is usually restricted to low yarn withdrawal
rates.

b) Over-end withdrawal.

In this system, the spool does not rotate. Therefore, the problems
associated with rotating a spool are avoided. The method is simple
and does not require driving the spool.

The disadvantage of this system is ballooning which is due to the

way the yarn is withdrawn and unwound from the package at high
speeds.

Centrifugal force causes the yarn to follow a curved path leading

to ballooning upon rotation of the yarn. Ballooning leads to
uneven tensions in the yarn. Each time one complete wrap of yarn
is removed from the supply package, the twist in that length
changes by one turn. These yarns cannot be unwound using the
over-end method; therefore, the side withdrawal method must be
used.

II- The tensioning and clearing region

In this region, proper tension is given to the yarn for a desired

12
package density and body. The typical components of this region
are a tension device, a device to detect thick and thin spots in the
yarn (clearing device) and a stop motion.

The stop motion causes the winding to stop in case of yam

breakage or the depletion of a supply package. The yarn is
directed into this region by a guide.

There are two types of guides (Figure 2.7): closed and open.

Figure 2.7
Closed guides require a yarn end to thread, and open guides do
not.
13
Open guides, however, give less positive guiding. Engineering
issues here are guide smoothness, abrasion between yarn and
guide causing yarn damage. If the guide is too rough, damage of
yarn due to abrasion will occur. On the other hand, if the guide is
too smooth, friction may develop. Guides are usually made from
hard stainless steels or from ceramics.
A. Tension device.
Yarn tension plays an important role in winding. Too high a
tension can damage the yarn, whereas too low a tension can lead
to unstable packages which will not unwind cleanly. Variations in
yarn tension in different parts of a wound package can cause
undesirable effects. For instance, with many man-made fibers,
high tension can cause molecular change which affects the
dyeability, so that variations in tension ultimately show as
apparently random variations in color shading.

The tension device maintains a proper tension in the yarn to

achieve a uniform package density. It also serves as a detector for
excessively weak spots in the yarn that break under the added
tension induced by the tension device.

There are three major types of tension devices (Figure 4.8).

14
 Figure 4.8
B. Yarn Clearers
The purpose of a yarn detertor is to remove thin and thick places.
Yarn detectors are usually two types: mechanical and electronic.
A mechanical clearer may be as simple as two parallel blades
(Figure 4.9).

15
 Figure 4.9
This type of device can only detect thick places in the yarn.

Electronic detectors are mainly two types: capacitive and photo-

electric (Figure 4.10).

Figure 4.10
In a capacitive type detector, the variation in the mass of the yarn
16
passing through the plates changes the capacitance of the unit. It
should be emphasized that the system measures the mass of the
yarn. When the generated signal reaches a certain value, the yarn
is cut.

In a photo-electric detector, the yarn passes between a light source

and a photocell. Any fluctuation in yarn thickness causes the
fluctuation of light coming to the photocell, which changes the
resistance of the photocell. This resistance change is detected by a
signal conditioning amplifier which can be set to send a signal to
cut the yarn and stop the winding process.

C. Stop motion.
The purpose of a stop motion is to stop winding when the yarn
breaks or runs out. Stop motions vary from machine to machine.

17
III- The winding region
In this region, the yarn package which is suitable for further
processing is wound. Many types of package configurations can
be obtained including cone, tube or cheese, dye tube or spool de-
pending on the next stage of processing.

The basic requirement of winding is uniform tension on the yarn.

Uniform tension is necessary for consistent winding and yarn
uniformity with respect to properties that are functions of tension.
If the tension on yarn passing the tension device is constant, the
tension in the package should be constant provided that the yarn
speed is constant, i.e., the tension on the package is only a
function of the yarn speed.

The rotation of the package may be accomplished in two ways:

spindle drive and friction drive.

1) Spindle drive winder (Figure 4.11). In this system, the spindle,

which holds the package, is driven directly. There are two
variations of this system: constant speed winders and variable
speed winders.

18
 Figure 4.11
2) Friction drive winder (Figure 4.12). In this system, the spindle,
that carries the package, is free to rotate and the package is driven
through surface friction between the package and a driven drum or
roller.

Figure 4.12
This system is widely used for staple yarns.
4.2.1.3 Yarn Traversing Mechanisms

A traversing mechanism is used to distribute the yarn axially along

the package. The distribution of the yarn should be done evenly on
the package.

In the friction drive winder, a traversing groove cut into the

19
friction drum is used (Fig.4.13). The yarn will fit into the groove
and travel back and forth along the length of the package as the
drum rotates.

Figure 4.13
In the spindle drive, a reciprocating traverse is used, i.e. an
externally driven guides the yarn back and forth across the
package (Fig.4.14)

Figure 4.14

20
4.2.1.4 Types of Packages
There are three fundamentally different types of packages:

a. the parallel wound package;

b. the near-parallel wound package;

c. the cross-wound package.

21
22
(a) The Parallel Wound Package.
This comprises many threads laid parallel to one another, as in a
warp. It is necessary to have a flanged package or beam, otherwise
the package would not be stable and would collapse (Fig. 4.15(a)).

Fig. 4.15

(b) The Near-parallel Wound Package

This comprises one or more threads which are laid very nearly
parallel to the layers already existing on the package. It may be
tapered, as in Fig. 4.15(b) or have flanges as in Fig. 4.15(a).

23
(c) The Cross-wound Package
This type usually consists of a single thread which is laid on the
package at an appreciable helix angle so that the layers cross one
another to give stability, as shown in Fig. 4.15(c).

The second and third types of packages require a traversing

mechanism on the winding machine to give the correct build.
Traversing methods are as follows

(1) Reciprocating
(a) Single guide rod and traversing cam serving many winding
spindles.

(b) A guide and cam for each spindle (Fig. 4.16).

24
 Figure 4.16
(2) Rotating
(a) Grooved roller with single groove (split drum).
(b) Grooved roller with multiple grooves (Fig. 4.17).

Figure 4.17
4.2.1.5 Winding Machines
Today’s winding machines allow use of different size bobbins
with different flange diameters, overall lengths and winding
widths on the same machine. For winding of industrial yarns such
as aramid, carbon or glass yams and monofilaments, specially
designed yarn guide elements are used. A spindle speed of 5000
rpm is possible.
25
Types
Winding machines in common use may be classified as;
Winding Machine

Manual Automatic

1. Small No. of Spindles 1. Travelling Spindle

Procating Traverse Circular

Rotating Traverse Elongated

2. Large No. of Spindles 2. Non-Travelling Spin.
Procating Traverse Small No. of Spindles

Rotating Traverse Large No. of Spindles

All the classifications can be further subdivided into cone and

cheese (spool) winders; generally, these are not mixed on any one
machine but it is possible for sections of some machines to
produce cones while others produce cheeses.
An automatic winder is commonly defined as a machine in which
creeling (including tying) and knotting of broken ends are
automatic but doffing is not necessarily so.

Automatic Winders with Traveling Spindles

26
4.2.1.6 Precision Winding
In precision winding, the position of the yarn as it is laid on the
package is controlled very precisely to increase the density of the
package. Figure 4.18 shows a precision winding machine. In this
particular machine, the yarn positioning system is all-electronic.
With the electronic system, freely programmable package building
is possible (Figure 4.19).

Figure 4.18

27
 Figure 4.19

4.2.2 Warping-Beaming

The purpose of warping (beaming) is to arrange a convenient

number of warp yarns so that they can be collected on a single
warper’s beam.

Today's warping machines can process all kinds of materials

including coarse and fine filament and staple yarns,
monofilaments, textured and smooth yarns, silk and other
synthetic yarns such as glass.

28
The warp beam that is installed on a weaving machine is called a
weaver's beam. A weaver's beam can contain several thousand
ends. There are several types of warping processes depending on
the purpose.

• Direct Warping (Beam warping)

• Indirect Warping (Sectional warping, conical drum, dresser
warping)
• Ball Warping
• Draw Warping
•

a. Direct Warping (Beaming)

Beaming is used for long runs of grey fabrics and simple patterns
where the amount of colored yarn involved is less than about 15
percent of the total. This is sometimes referred to as direct
warping.

In direct warping, the yarns are withdrawn from the single-end

yarn packages on the creel and directly wound on a beam (see
Figure 4.20).

29
 Figure 4.20 Direct warping
This kind of warping is carried out in two separate stages:

1) Direct warping can be used to directly produce the weaver's beam

in a single operation. This is especially suitable for strong yarns that
do not require sizing such as continuous filaments or monofilaments
and when the number of warps ends on the warp beam is relatively
small. This is also called direct beaming.

Many beams are prepared as indicated by the result of following

expression.
Number of beams = Total number of warp yarns / creel capacity

2) Direct warping is used to make smaller, intermediate beams called

warper's beams. These smaller beams are combined later at the

30
slashing stage to produce the weaver's beam. This process is called
beaming (Figure 4.21).

Figure 4.21 Beaming

Direct warpers are used to warp all conventional staple fibers,

regenerated fibers and filaments. In direct warping, a flange beam is
used. Since all the yarns are wound at the same time, the flanges
provide sufficient yarn stability on the beam. The typical beam flange
diameters are 800, 1000, 1250 and 1400 mm with working widths of
1400 to 2800 mm.

b) Indirect (Section) Warping

31
It is used for short runs, especially of fancy patterned fabrics
where the amount of colored yarn is greater than about 15 per cent
of the total. This is sometimes referred to as indirect warping or
pattern warping.

Other names used for section warping are pattern warping, band
warping or drum warping. It is cost-effective for short and striped
warps (cotton and wool fabrics).

The section beam is tapered at one end. Warp yarn is wound on the
beam in sections, starting with the tapered end of the beam (Figure
4.22).

Figure 4.22 Schematic of yarn sections on tapered section beam

Each section has multiple ends that are traversed together slowly
during winding along the length of the section to form the angle.

Before carrying out warping, following calculations are necessary:

32
Section number = Total number of warp threads /creel loading
capacity

If the calculation does not give an exact number, the last section
will be produced with a number of threads lower than the other
sections
Section width =Reed width / Number of sections

c.) Ball Warping

Ball warping is mainly used in manufacturing of denim fabrics. The
warp yarns are wound on a ball beam in the form of tow for indigo
dyeing (Figure 4.23).

Figure 4.23 Winding on ball beam

d.) Draw Warping
Draw warping is combining the drawing of filament yarns with
heat setting and warping processes to achieve uniform stretching
and heating for improved dye uniformity, end to end. It is used for
weaving of thermoplastic yarns. Figure 4.24 shows schematic of

33
draw warping process. Typical speed is up to 1000 m/min. Single
or two phase drawing is possible

Figure 4.24
4.2.1 Warping Machines
A typical warping machine has three major components:
a. creel,
b. headstock and
c control devices.
a. Creel
Independently of the warping system, the threads are fed from
bobbins placed on creels. The creels are simply metallic frames on
which the feeding bobbins are fitted; they are equipped with yarn
tensioning devices, which in modern machines are provided with
automatic control and centralized tension variation.

34
The creel capacity is the parameter on which the number of
warping sections or beams depends; it should be as high as the
installation type and planning permit; the usual creel capacity
amounts today to 800-1200 bobbins.

Various solutions have been designed to reduce the time required

to load the creel and thus increase the warping performance.
There are various types of creels. The most common creel types
are:
• parallel standard creel with fixed package frame (single end
creel)
• parallel creel with package trucks
• parallel creel with swivelling package frame sections (for cotton,
viscose, polyester/cotton, wool colored)
• V-creel with reversible frames
•V-creel with reversible frames and automatic knotter (for
cotton, viscose, polyester/cotton)
• V-creel with traveling packages

Parallel creels are used for sectional warping and direct warping;
V-creels are used for direct warping.

35
 Figure 4.25 Trolley Creel (Mobile Creel)
Trolley creels are suitable for both sectional and direct warping.

In a magazine creel, usually a two package creel is used. Figure

4.26 shows a magazine creel with two pivoting spindles: a
working spindle and a reserve spindle. When one set of spindles is
in operation, the empty packages are removed from the reserve
set, which is then filled with new packages.

36
 Figure 4.26 Magazine Creel
In the swivel frame creel, empty packages can be replaced on either
side from the center aisle. This creel is suitable for confined spaces.
A foot pedal is used to swivel the frame 180° to allow the empty
side to be recreeled (Figure 4.27). Swivel creels can have a V
shape as well.

37
 Figure 4.27 Swivel Frame Creel
In traveling package creels (V-shaped creel), the creel is like a
continuous belt as shown in Figure 4.28. Usually two creels form a V
shape.

Figure 4.28 V-shaped creel

38
Advantages of V-creel are:
• no need for yarn guide
• uniform yarn tension across the whole beam
• free yarn run from the creel to the warping machine
• low yarn tension

b. Headstock
It is a requirement that the yarn speed should be kept as constant as
possible during warping and there are several ways of achieving
this.

In indirect (section) warping, a constant speed drive is generally

sufficient in providing approximately uniform yarn speed on the
surface of the beam. This is because the thickness of the yarn built
on the beam is relatively small compared to the beam diameter such
that the surface speed does not change much.

In direct warping, the change due to yarn buildup on the beam is

significant. Therefore, in direct warping, mechanisms that are
similar to the ones used in winding are utilized to attain uniform
yarn speed; surface friction drive and variable speed drive are
commonly used. For some filament yarns, variable speed drive is
chosen since friction drive would cause problems.

39
Today's headstocks are equipped with advanced design features
such as precision direct drive, advanced electronics, smooth doffing
and programmable breaking.

c. Control Devices

Similar to winding, warp yarns are threaded through tension

devices, stop motions, leasing rods and the reed. Uniform tension is
necessary so that all the warp ends behave the same way. The
tension on the warp yarns is kept relatively low. Every end requires
a tension controller that is usually located close to the package.

Figure 4.29 shows an electronic, motion sensitive stop motion device.

The electronic eye detects movement of individual ends to trigger a
warp stop when there is no yarn movement.

Figure 4.29

40
Figure 4.30 shows mechanical stop motions, drop wire and faller
wire.

Figure 4.30
Figure 4.31 shows the schematic of a vibration sensitive yarn stop
motion for creels. The sensor detects the motion of yarn, not the
presence of the yarn.

Figure 4.31

Figure 4.32 shows a mechanical stop motion and yarn clamping

system.
41
 Figure 4.32
Tension Control in Warping
Several tensioning devices are used for unwinding of packages in
warping. Figure 4.33 shows a roller tension unit that is used for
warping.

Figure 4.33

42
The roller tension unit is suitable for yarns of 180 dtex or higher. All
staple yarns and continuous filaments with or without twist can be
handled. The maximum working speed is around 800 m/min.

Figure 4.34 shows a capstan tensioner for warping of fine yarns.

The yarn guidance element is a capstan roller that is rotated by several
winds of unwinding yam wrapped around it.

Figure 4.34
The major advantage of this tensioner is that it does not wear the yarn;
it can be used for 10-830 dtex yarns. The maximum working speed is
around 800 m/min.

The disc tensioner is good for all types of yarns, 100 dtex and
higher, at high speeds, up to 1200 m/min (Figure 4.35). The yarn
tension is adjusted by a tension spring with the aid of an angle lever.

43
 Figure 4.35
Figure 4.36 shows the schematic of a patented internal intermittent dust
blowing system to prevent fly accumulation in the tension unit.

Figure 4.36
Figure 4.37 shows a relatively simple system to control the
tension. Yarn enters the tensioner at the bottom and runs through
the surface of the ball(s). As the incoming tension is increased, the
yarn has to lift the balls higher against the gravity. As a result, the
yarn will use up its extra energy to move the balls inside the
cylinder. This will result in compensation of the high tension.

44
 Figure 3.37
Figure 4.38 shows another compensating yarn tension regulator,
which compensates yarn tension differences between full and
empty yarn packages, in a speed range of 200-1200 m/min. Tension
peaks are absorbed by means of permanent magnet damping action
of the compensating lever.

Figure 4.38
.
45
4.2.3 Warp Sizing (Slashing)

The Need for Slashing Although the quality and characteristics

of the warp yarns coming out of the winding and warping
processes are quite good, they are still not good enough for the
weaving process for most of the yarns. The weaving process
requires the warp yarn to be strong, smooth and elastic to a certain
degree. To achieve these properties on the warp yarns, a protective
coating of a polymeric film forming agent (size) is applied to the
warp yarns prior to weaving; this process is called slashing or
sizing.

The main purposes of slashing are as follows:

to increase the strength of the yarns§to reduce the yarn hairiness
that would cause problems in weaving process§to increase the
abrasion resistance of the yarns against other yarns and various
weaving machine elements§ to reduce fluff and fly during the
weaving process for high speed weaving machines
The ultimate goal of sizing is to eliminate or reduce warp breaks
during weaving. Warp breaks are caused either by high tension
or by low strength in the yarn. High tensions in the warp are
caused by § large shed openings, high beat-up force,
inadequate let-off,

46
Knots, yarn entanglement and high friction also cause tension
buildup
There are three types of tension on a warp yarn during
weaving: §constant mean tension,§cyclic tension
variations§random tension variations

The warp is under constant tension on the loom and the

magnitude of this tension is generally determined by the take-
up/let-off rate, crimp developed during weaving and elasticity rate
of the warp yarn. Mean tension is usually not the cause for warp
breakage.
Cyclic tension variations are caused by §shedding §beat-up.
Tension patterns due to shedding and beat-up depend on the fabric
design and structure. Warp tensions due to shedding and beat-up
are so high that they have to be compensated by tension
compensation devices; however, it is hardly possible to eliminate
them entirely.
Random tension variations are caused by different reasons such
as §an improper knot,§entanglement of warp yarns due to
protruding fibers, etc. A thick knot may not pass through the
heddle eye or reed easily which causes the tension to build up. The
warp yarns follow a tortuous path that includes tension and
abrasion zones on the loom during fabric formation

47
Several spun yarn properties are positively affected by
slashing
§reduce hairiness, §improve strength and abrasion resistance
§elongation is reduced in a controlled manner
§flexibility is reduced but reasonably maintained.
Necessary Terms
§Size concentration: the mass of oven dry solid matter in size
paste.
§Size take-up (size add-on): the mass of paste taken up in the size
box per unit weight of oven dry unsized yarn.
§Size percentage: the mass of oven dry size per unit weight of
oven dry unsized yarn.
Slashing Machines
A slasher machine is used to apply the size
material to the yarns. The major parts of theslasher are;
§creel, §size box, §drying units, §beaming, §various control
devices
The critical parameters to watch in the sizing process are;
§ size homogeneity, § constant speed of the sizing machine,§
constant size concentrations § viscosity§ temperature of the size
box is important for proper size pick up. §
Selecting of a Sizing Machine
Selection of a sizing machine depends on several factors,
including;
48
§warp specifications, §weaving requirements and §production
volume.
The output of the sizing machine is determined by the size of the
dryer.

IMPORTANT NOTES
It should be noted that only warp yarns need to be sized. Because
warp yarns are subject to harsher treatments than filling yarns
during the weaving process on the weaving machine.
It is important that the size film must coat the yarn surface without
excessive penetration into the body of the yarn, because if the size
material is penetrated deep in the yarn, complete desizing would
not be possible.
Although sizing is done mainly to increase the strength of the
yarn, some strong yarns such as continuous filaments still need
sizing. This is because sizing keeps the slack and broken filaments
together in low twist yams.

Important Points of Slashing

§Slasher creel tension control is critical. Maximum tension should
not exceed 5% of breaking strength.§The amount of size picked
up is affected by the viscosity of the size mix and the yarn
structure. §Yarn spacing at the slasher size box and on the drying
cylinders is very important.
49
§Stretch of warp yarns during slashing should be controlled
accurately to maintain residual elongation in the yarn which is
needed for good weaving.
§Guide rollers should be kept free from nicks, burrs and sharp
edges.§Pre-wetting yarns prior to sizing can reduce the amount of
required size add-on for the same performance, especially for
cotton yarns.§Water soluble sizes can cause problems in water jet
weaving.§
Choosing the Proper Chemistry for Sizing

Several factors should be considered when choosing the size

mixture:§yarn material (cotton, poly/cotton, polyester, rayon,
wool, etc.)§yarn hairiness§yarn structure (ring spun, open-end, jet
spun)§water to be used for cooking (recycled or fresh)§type and
speed of weaving machines to be used (projectile, rapier, air-jet,
water-jet)§% add-on (and % solids) required

§yarn occupation in the size box and on the dry cans§desizing

procedures§reclamation of size and use of enzymes in the
finishing plant§slasher design and number of size
boxes§environmental restrictions

Filament Sizing

50
Twisted and zero-twist filament yarns can be sized. The
continuous multifilament yarns are generally smooth and have a
surface finish that protects the yarns against abrasion and static
during processing. Because of their smooth and lubricated
surfaces, high twist filaments may not require sizing. However,
low twist multifilaments should be sized because if a single
filament breaks, it can develop a fuzz ball, float or skip that will
ultimately cause a loom stop.
Size requirements for filament yams are as follows : §The size
solution must sufficiently penetrate the filament bundle. §The
adhesion between the filament and size must be good.§The sizing
agent must dry quickly enough without producing a tacky surface.
Size requirements for filament yams are as follows : §The
elasticity and flexibility of the size film should match to those of
the yarns under weaving stresses.§The size should not cause static
build up.§The size should not shed excessively causing a build up
on the heddles, reeds or other weaving machine parts.§Size film
properties should not be affected drastically by extreme humidity
changes.§The size should be easily removable during desizing.
§The size should not cause adverse effects on the yam, processing
equipment or human health.§The size should be easy to process
and use.§The producer spin finish oils should not affect the size
properties.§Sizes may foam at high machine speeds. To prevent
this, anti-foaming agents can be used.
51
Desizing

After weaving, the size must be removed from the fabric in the
finishing process. If the size is not recovered then the effluent
from the finishing plant will contain the size and should be treated
before it can be discharged. Ease of size removal and the cost of
desizing are different for each size material. The type of
ingredients in the size mixture is also critical. They affect the
finishing process since these materials should be completely
removed before other finishing and dyeing processes.

Fabrics with starch sizes are treated with chemicals that break
down both the linear and branched chains into shorter fragments.
Starch is a carbohydrate. Therefore, it can be broken down similar
to a starch eaten by animals and bacteria. Weak acids and enzymes
are used to break down the starch chain structure without
damaging the cotton cellulose. As a result, the chains are broken
down into smaller water soluble fragments that are washed away.
The desizing process can proceed at a faster rate at higher
temperatures.
Since PVA forms true solutions with water, it is only required that
the polymer redissolves in the hot water during desizing. That is, it
is not necessary to degrade the PVA chains in order to remove the
52
size film, allowing the recovery of the size by one of several
recovery processes for reuse. This is an important advantage of
PVA because some textile companies recover and reuse PVA
sizes.

During the desize operation of polyacrylic acid based sizes, the

size is resolubilized using an alkaline desize. A solvent desize may
be necessary for acetate yams. Some industrial fabrics need
not to be desized. For example, for some coated fabrics, the
adhesion of the PVA size is needed as a primer coating for
adhesion to the coating. However, this requires a more uniform
size application than normal.

It is necessary to size the warp yarn for several reasons, namely:

- To strengthen the yarn by causing the fibers to adhere
together;
- To make the outer surface of the yarn smoother so that
hairs protruding from one yarn in the warp should not
become entangled with hairs protruding from a
neighboring yarn;
- To lubricate the yarns so that there is less friction when
they rub together in the weaving process. Lubrication
also reduces the friction between the yarns and the loom
parts. The reduction of friction reduces the forces acting
53
on the yarns during weaving.

54